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Figure from:Stereopsis: Important Papers

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Figure 4 Panum’s fusional area is illustrated here in gray. Within this region (exaggerated here for purpose of exposition) points such as P, which lie off the horopter, H, have binocular disparity but are seen as single and in depth relative to the fixation point, F.

Related Figures (13)

Figure 1 A stereoscopic image pair taken with two cameras. Right eye view on the left, left eye view on the right. To view, cross your eyes, until the two squares align, and focus on the middle image. Courtesy of Zeb Hodge, as posted on Flickr.

Figure 3 The horopter and crossed vs. uncrossed disparities. The horopter is the set of points having zero binocular disparity, given by the dotted arc passing through the fixation point, F. In this example, L and M lie on the horopter while P (with uncrossed disparity) and C (with crossed disparity) do not.

Figure 2 The geometry of binocular disparity. The two eyes view a point P while fixating point F, at distance d from the observer. The distance between F and P is given by Ad and the interocular distance is iod. Angles w and 0 give the angular subtense of points F and P, respectively.

Figure 5 Wheatstone’s diagram of his stereoscope as published in 1838. A’ and A are mirrors, which reflect images of the stereo pair (E’, E) separately to the two eyes. The same principle is used in laboratories today.

Figure 6 A simple line stereogram. By cross-fusing (left image to right eye, right image to left eye) the two dark frames and the central dot, the relative depth of the unfilled bars become apparent. The upper bar should appear closer to the observer than the central dot and frame, while the lower bar should appear further away.

Figure 7 A random-dot stereogram image similar to that presented by Julez in 1964. By cross-fusing this stereo pair, one can observe a central square region displaced in depth in front of the surrounding region.

Figure 8 Stimuli adapted from, and thresholds (in seconds of arc) reported by Suzanne McKee in 1983. In each instance the two vertical lines are displaced in depth to assess stereoacuity and are identical in all conditions (a—e).

Fig. 1. Schematic geometry of the Howard-Dohlman stereoacuity test. Peg A is fixed at a distance z from the observer, whose left (L) and right (R) eyes are a distance a apart. The observer's task is to set peg B so that it is just discriminably nearer than A. The binocular parallax of A, in radians, is a/z. With respect to A, B has disparity Ay = a/z?)Az.

Fig. 2. Three-line stereogram in which the relative placement of the lines in the right and left panels cannot be used by even a knowledgeable observer for a reliable judgment of their depths.

Fig. 3. Sample line of a right/left pair of stereogram panels for a stereoacuity test in which stimulus conditions are optimized. Sharp, clearly separated features are members of ensembles already known to the patient (alphanumeric characters or geometrical shapes). One symbol in each row has disparity and should be recognized as either in front or behind the rest. Locations in row are not quite regular so that lateral position cannot be used as a depth clue. Vertical arraying of such rows with progressively diminishing disparity would generate a chart that can be utilized in the manner of the Snellen chart for visual acuity.

they are almost impossible to see. When approached, they almost never move, but can make a buzzing sound that resembles bees, presumably to ward off predators. Their prey as well as their predators are fooled by the plumage. When a prey moves into range, the bird attacks and dispatches the prey quickly even using the stiff whisker-like feath- ers (see BJO April 2001 for discussion of avian feathers) around their beaks to assist in capture. Their feet are weak and do not assist in capture, but with the large, sturdy, triangular hooked bill, the feet are unnecessary for the kill.

Barn owl eye. Note the asymmetrical globe with a large equatorial diameter.

Figure 1 Olfactory organs to absorb scent (olfactory rosettes) in Sphyrna lewini as illustrated by white arrows, and optic nerves with blue arrows (computed tomography scan with false colour). -— Sewer eee Florida Atlantic University, Florida, USA Much like other elasmobranchs, sharks accommodate using a protractor lentis, which pulls the lens away from the retina as compared with teleosts (bony fish) that have a retractor lentis muscle that moves the lens towards the retina (BJO April 2006). This suggests that the last common ancestor of sharks and teleosts, mentioned above, probably had rudimentary, if any, accommodation. Accommodation must

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